1. Field of the Invention
This invention is related to a process for the extraction and elimination of deleterious material present in natural manganese dioxide (NMD), as well as in natural concentrated manganese dioxide obtained by said process.
2. Description of the Related Art
Natural manganese dioxide (NMD) is frequently used in the manufacture of electrochemical batteries. However, NMD normally contains a very high content of deleterious material, such as copper, nickel, cobalt, iron, aluminum, potassium, and the like, which is highly undesirable to manufacturers of such electrochemical batteries. The deleterious material, mainly the heavy metals, drastically reduces the discharging performance of the electrochemical batteries, while significantly increasing the corrosion thereof.
The process of hydrochloric acid (HCl) leaching of manganese ore has been described in several documents, especially in documents published in the late 1960's and early 1970's, when a large surplus of HCl derived from polyvinyl chloride (PVC) processing was available. Such leaching processes were based on the manganese ore being treated with an HCl solution under certain reaction conditions, especially temperature and HCl concentration. Examples of patents, which disclose such process are AU Patent 435 309, U.S. Pat. No. 3,437,345, published Application DE 2 164 799, U.S. Pat. No.3,770,868, and U.S. Pat. No. 4,872,909. Other references similarly processes for leaching of manganese dioxide, such as "A New Process for the Production of Synthetic Battery grade Manganese Dioxide", National Chemical Engineering Conference, Surfers Paradise, Queensland, (1974). All such references, which represent the state of the art processes for the leaching of manganese dioxide, denote that the interesting phase of such process is the liquid i.e., the leaching phase. Therefore, the concentrate or solid residue of non-leached manganese dioxide in such process has a high concentration of deleterious material and, as a consequence, a low concentration of MnO.sub.2, which, as mentioned above, is highly undesirable. There is no known process for the leaching of NMD ore which supplies, in industrial quantities, a concentrate of manganese dioxide having acceptable levels of deleterious material and which retains its original crystalline structure.